The invention relates to drawing apparatus in presses, having a pressure cheek for holding the metal sheet during the drawing operation, separately adjustable pressure cylinders which, by way of the pressure cheek, act upon metal-sheet holders in the tools locking cylinders for a controlled raising of the metal-sheet holder after the drawing operation.
Drawing devices are used for generating metal-sheet holding forces during the deformation (drawing) and during the ejector movement (raising) of the drawn part from the tool of a press. During the drawing operation, the metal-sheet holding forces or counterholding forces are applied by pressure cylinders the pressure of which can be individually adapted to the drawing requirements, which are designed for the avoidance of cracks and folding. The ejector movement for the raising of the formed drawn part is controlled by means of locking cylinders.
From European patent document EP 0173 755 A1, it is known to adapt the metal-sheet holding forces in the various contact pressure ranges before and after the deformation. On the basis of the German patent document DE 35 05 984 A1, it is known, in the case of a drawing apparatus, to control the ejector movement of the metal-sheet holder in a time-delayed manner to the upward movement of the slide and the speed of the ejector movement. Additional control measures for metal-sheet holder are disclosed in German patent document DE 38 07 683 A1. Thus, for example, the movement and the stop of a pressure cylinder piston is used for limiting the movement of the piston of another pressure cylinder, in this case, of a drawing cylinder. In addition, this text shows a divided pressure cheek the segments of which can individually be acted upon by pressure.
German patent document DE 28 06 528 B 2, discloses a device for the mechanical height adjustment of four pressure points of a metal-sheet holding device. However, the object according to the invention is not achieved by this measure in the case of drawing apparatus of this type.
It is an object of the invention to interrupt the ejector movement of the pressure cylinders in a preselected position, for example, after 10 mm, and to resume the raising movement for the pressure cheek at a later time-delayed moment. In this case, the starting position for the beginning of the drawing must be controllable, and the lower dead center for the drawing apparatus must be adjustable to the tool requirements.
In a drawing apparatus of the above-mentioned type, this object is achieved in that each of the segments of the pressure cheek, in a sensitive manner, can be adjusted to the requirements of the drawing in partial areas of the drawn part. The console, which is common to all piston rods and all pressure rods, permits a joint control of the upward movement of all pressure rods. The valve control permits a precise maintaining of the predetermined detent point of the ejector movement.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.